Cocoa, the key flavour in chocolate, could be good for your memory, too. Photo: AFP

The study – published online on Sunday in Nature Neuroscience and partly financed by a chocolate company – has found that flavanols reverse mild memory loss in older adults.

Using brain scans and memory tests, the latest study built on previous work showing that flavanols extracted from cocoa beans had improved neuronal connections in mice's dentate gyrus, a part of the brain involved in memory formation.

But hold that chocolate bar. The researchers also warn that the compound found in cocoa exists only in minuscule amounts in the average chocolate bar compared with the amount used in the study, so gorging on chocolate in the name of health and improving one's memory could backfire.

"It would make a lot of people happy but it would also make them unhealthy," Scott Small, a professor of neurology and director of the Alzheimer's Disease Research Centre at the Taub Institute at Columbia University Medical Centre, said on Friday.

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Professor Small said that even more important, the new study offered the first direct evidence that memory deteriorated with age because of changes in the dentate gyrus, a region of the hippocampus.

Previous studies had shown a link between changes in this region of the brain and normal, age-related memory loss. However, the Columbia University study asserts a causal link.

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"It more firmly establishes that this is the anatomical source of age-related memory loss," Professor Small, the study's senior author, said.

He said the study also offered yet more evidence that diet and healthy lifestyles that increased blood flow to the brain could slow or reverse age-related cognitive decline.

The study involved 37 healthy subjects aged from 50 to 69. On a random basis, they were given either a high-flavanol diet, consuming 900 milligrams a day, or a low flavanol diet, consuming 10 milligrams per day. Brain scans, which measure blood volume in the dentate gyrus, and memory tests were used to evaluate the effect of the diet.

Professor Small said the typical candy bar contained about 40 milligrams of flavanols.

Researchers said that if a person had the memory of a typical 60-year-old at the beginning of the study, after three months, on average, that person's memory would function more like that of a 30-year-old or 40-year-old person.

The researchers also cautioned that more work was needed because of the study's small sample size.

The compounds appear to enhance connectivity and metabolic activity in the dentate gyrus. Ageing appears to reduce the synapses, or connections, between neurons in that part of the brain.

However, that decline, was not related to severe memory loss and cell death in Alzheimer's disease or other dementias, Professor Small said.

Most cocoa-processing methods in use today remove many of the flavanols found in cocoa.

However, chocolate maker Mars produced a cocoa flavanol test drink specifically designed for the research, which the company also subsidised.